The present invention relates to circuit breaker motor operator control circuits, and particularly to a motor operator circuit for controllably energizing an AC motor from an AC source.
It has been common practice to utilize DC motors in circuit breaker motor operators because of their inherent capability of being readily and precisely controlled, particularly in terms of conveniently braking such motors to an abrupt halt using a purely electrical, dynamic braking approach. For example, as disclosed in my co-pending application, Ser. No. 889,755, filed Mar. 24, 1978, a circuit breaker motor operator utilizing a permanent magnet DC motor can be readily braked to a precise stop simply by interrupting DC current to the motor and switching in a braking resistor across the motor armature. The motor thus is effectively converted to a DC generator operating to pump current through the braking resistor, and its output shaft is dynamically braked to an abrupt halt, e.g., in considerably less than one second.
Unfortunately, a suitable source of DC current to power a circuit breaker motor operator is typically not readily available. Under these circumstances, AC current must be utilized, necessitating the additional expense of full-wave rectifying bridges. Energization of DC motors from a full-wave rectified AC voltage, with its inherent ripple, produces excessive arcing which drastically reduces the life of a DC motor. Adequate filtering to smooth out this ripple requires an electrolytic capacitor, which is relatively expensive and has packaging drawbacks due to its relatively large physical size. Electrolytic capacitors have the additional drawback by the propensity for losing their dielectric properties during prolonged periods of de-energization. Since circuit breaker motor operators are typically called upon to operate rather infrequently, this drawback is a significant one.
Accordingly, it is an object of the present invention to provide an improved motor operator control circuit.
A further object is to provide a motor operator control circuit of the above character which is equipped to controllably energize an AC motor from an AC current source.
An additional object is to provide a motor operator control circuit of the above character capable of instituting dynamic braking of an AC motor, pursuant to precisely braking the motor output shaft to an abrupt halt.
Yet another object is to provide a motor operator control circuit of the above character having particular application in circuit breaker motor operators.
A further object is to provide a circuit breaker motor operator control circuit having anti-pumping provisions.
Still another object of the present invention is to provide a circuit breaker motor operator control circuit of the above character which is inexpensive to manufacture, efficient in construction and reliable in operation.
Other objects of the present invention will in part be obvious and in part appear hereinafter.